Large marine predators, including great white sharks, have been discovered venturing into the depths of the ocean where they do not typically feed. A recent study analyzed the behavior of 12 species of large predatory fish and found that they regularly spend time in the mesopelagic zone, also known as the twilight zone, which is located between 656 and 3,280 feet beneath the ocean surface. Additionally, these predators were observed in the midnight zone, which extends from 3,280 to 9,800 feet below the surface.
To determine the diving patterns of these predators, researchers compared the movements of 344 electronically tagged fish with shipboard sonar data. By doing so, they were able to identify which species frequently dive into the twilight and midnight zones. The study also revealed a correlation between these dives and the location of the deep scattering layer (DSL), which is a densely packed ocean layer containing numerous small fish and other organisms. At night, the DSL rises to the surface for feeding, only to sink back down into the twilight zone during the day.
This research suggests that marine predators often feed on animals in the DSL, yet it also found that many predators dive even deeper than the DSL extends. For example, great white sharks were observed diving as deep as 3,700 feet, whale sharks reached depths of 6,300 feet, and swordfish descended to 6,500 feet. While some dives appeared to be for foraging purposes, others did not involve feeding, indicating a different type of predator-prey interaction.
The study highlights the importance of the twilight zone as a vital habitat for large predator species. Furthermore, many commercially fished species inhabit this zone, emphasizing the necessity to comprehend and protect this unique ecosystem. Currently, the twilight zone is estimated to contain more biomass than all existing marine capture fisheries combined, which raises concern about the potential exploitation of this resource. However, before any sustainable harvesting can take place, it is crucial to quantify the connections between predators and mesopelagic biomass.
In conclusion, the discovery of large marine predators spending time in the twilight and midnight zones sheds light on an overlooked habitat. The study’s findings underscore the importance of understanding and safeguarding the twilight zone, as well as the need to further investigate the relationships between predators and the abundant biomass present in this unique ecosystem.
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